WASHINGTON
— With tomorrow's committee vote on three of President Bush's most controversial judicial nominations, the Senate - urged on by some of the most powerful interests in Washington - is poised for a long-awaited showdown over the federal courts.

Each has been nominated before - and denied a vote on the floor of the Senate based on arguments ranging from incompetence to extremism. But this time, Senate GOP leaders say a Democratic filibuster will not stand. They threaten a rule change that Democrats warn will shut down the Senate.

Until now, Judiciary chairman Arlen Specter (R) of Pennsylvania had moved to a committee vote only those nominations that he expected could win enough bipartisan support to avoid a filibuster. With Thursday's vote, that strategy ends - a move that could signal that the so-called "nuclear option" is imminent. That proposed rule change would lower the number of votes required to end debate on a nomination from 60 to a simple majority. "It does appear that the Republicans are moving forward on the nuclear option," says Jonathan Turley, a law professor at George Washington University Law School. "The White House has clearly decided that it would be better to fight this fight now rather than with a Supreme Court nominee."

By the pound, Priscilla Owen, nominee for the US Court of Appeals to the Fifth Circuit, faces the toughest confirmation fight. Her bulging opposition file, provided by minority Democrats, weighs in at 4.8 lbs and includes letters from more than 40 national groups ranging from Planned Parenthood and Friends of the Earth to the United Auto Workers. The opposition file for Janice Rogers Brown, a nominee to the District of Columbia Circuit, tops 3.5 lbs. In contrast, the file for Terrence Boyle, a nominee to the 4th Circuit, weighs less than a pound.

It's a high-stakes battle, managed with an intensity once reserved for controversial Supreme Court nominees. In addition to the flood of faxes, floor statements, and news releases inside Congress, interest groups are accelerating ad campaigns to engage the public and pressure would-be compromisers on both sides. With at least one vacancy on the Supreme Court expected this summer, analysts say the positioning on these three appeals court nominees is a proxy fight for other battles to come.

"I think there is a realization that the court of appeals are in effect our regional Supreme Courts," says Sheldon Goldman, an expert on judicial nominations at the University of Massachusetts at Amherst. "It's the end of the line for 99 percent of all appeals. And it has become clearer and clearer that these judges have wide discretion in interpreting the Constitution, precedents and statutes."

A filibuster of any one of the president's nominees could provide the context for invoking the nuclear option, but the two women nominees, Ms. Owen and Ms. Brown, are the highest-profile cases.

A justice on the Texas Supreme Court since 1995, Owen has had two confirmation hearings: one in 2002, when the committee was controlled by Democrats, and another in 2003, after Republicans had taken back the Senate.

At that hearing, dubbed "setting the record straight," then-Judiciary Committee chairman Orrin Hatch called her treatment by Democrats a "disgrace to the Senate." Owen was the first nominee with the American Bar Association's highest rating to be voted down by the committee, he said.

In response, Democrats noted that two of President Clinton's nominees for the same vacancy, Judge Jorge Rangel and lawyer Enrique Moreno, were both denied even a hearing on their nominations when Republicans controlled the Senate.

Owen, critics say, is a judicial activist whose record shows a bias against the environment and victims of discrimination and medical malpractice. But the most telling critique of the Owen record comes from a voice now inside the Bush administration. As a colleague on the Texas Supreme Court, Attorney General Alberto Gonzales once criticized Owen for an "unconscionable act of judicial activism" by restricting a minor's access to abortion. He now supports her nomination enthusiastically, but the old rebuke still replays often in the debate over her confirmation.

Mr. Boyle, a Reagan appointee, has been a federal district court judge in North Carolina since 1984. His conservative credentials include a brief stint as legislative assistant to former Sen. Jesse Helms in 1973, but critics say the issue in this case is competence, not ideology. Despite a "well qualified" rating from the American Bar Association, Judge Boyle has had 139 of his cases reversed. These range from cases involving age, gender, and racial discrimination to the rights of public employees, according to filings with the Senate Judiciary Committee.

Boyle was first nominated to the Fourth Circuit in 1991 by the first President Bush, but the Judiciary panel, then controlled by Democrats, let his nomination lapse. He was renominated in 2001 by the second President Bush, but the nomination was blocked by then-Sen. John Edwards. It's a probable target for a filibuster on the Senate floor.

In opposing the nomination of Ms. Brown, who holds a seat on the California Supreme Court, critics cite positions hostile to consumer protection, worker protection, and the environment. But much of the fireworks has been over her remarks outside the courtroom, including a reference to the New Deal in a 2000 speech as a "socialist revolution."

This week, MoveOn PAC, a liberal advocacy group, launched a 10-day campaign to block her nomination and the nuclear option. At the same time, supporters within conservative, business, and the evangelical communities are ramping up their own media campaigns in support of the president's nominees.

"If you examine somebody's record long enough, you can always find something in anyone's background to point to," says Larry Sabato, a political scientist at the University of Virginia. "But these are conservative Republicans who are going to rule pretty much the same way as the other Bush appointees who have won their seats on the federal bench."

Supporters say that all three are highly qualified jurists whose records have been unfairly distorted. "When well over 50 percent or over 60 percent of the citizens in those states [California and Texas] vote to support these judges to continue in office on their state supreme court, you'd hardly say that these nominees are out of the mainstream," said Sen. Jon Kyl (R) of Arizona, in a floor statement on Monday.